Seatbelt pretensioning retractor assembly including a piston-safety valve member

ABSTRACT

A seatbelt pretensioning retractor assembly for use in a passenger vehicle is provided. The pretensioning assembly includes a tube in fluid communication with a gas generator and a driving element disposed therein that travels in a first direction in response to actuation of the gas generator. The driving element includes a polymer rod. A stopper is coupled to a proximal end portion of the polymer rod. A piston-safety valve member is disposed between the gas generator and the stopper and is configured to allow gas from the gas generator to pass therethrough when the gas is at or above a predetermined pressure.

TECHNICAL FIELD

The technical field relates generally to seatbelt restraint devices forrestraining an occupant of a vehicle, and more particularly, to devicesfor pretensioning a seatbelt.

BACKGROUND

Seatbelt restraint systems for restraining an occupant in a vehicle seatplay an important role in reducing occupant injury in vehicle crashsituations. Seatbelt restraint systems of the conventional so-called“3-point” variety commonly have a lap belt section extending across theseat occupant's pelvis and a shoulder belt section crossing the uppertorso, which are fastened together or are formed by a continuous lengthof seatbelt webbing. The lap and shoulder belt sections are connected tothe vehicle structure by anchorages. A belt retractor is typicallyprovided to store belt webbing and may further act to manage belttension loads in a crash situation. Seatbelt restraint systems which aremanually deployed by the occupant (so-called “active” types) alsotypically include a buckle attached to the vehicle body structure by ananchorage. A latch plate attached to the belt webbing is received by thebuckle to allow the belt system to be fastened for enabling restraint,and unfastened to allow entrance and egress from the vehicle. Seatbeltsystems, when deployed, effectively restrain the occupant during acollision.

OEM vehicle manufacturers often provide seatbelt restraint systems withpretensioning devices, which tension the seatbelt either during animpact of the vehicle or even prior to impact (also known as a“pre-pretensioner”) to enhance occupant restraint performance. Thepretensioner takes out slack in the webbing and permits the beltrestraint system to couple with the occupant early in the crashsequence. One type of pretensioner acts on the webbing retractor totension the belt. Various designs of retractor pretensioners presentlyexist, including a type known as a roto-pretensioner that incorporates agas generator for generating a pyrotechnic charge. Examples of suchroto-pretensioners are described in U.S. Pat. No. 5,881,962, filed Apr.11, 1995, U.S. Patent Application Publication No. 2006/0243843, filedApr. 27, 2005, U.S. Patent Application Publication No. 2012/0006925,filed Jul. 6, 2010, and U.S. Pat. No. 7,988,084, filed Aug. 2, 2011,which are commonly owned by the assignee of the present application andare hereby incorporated by reference in their entirety for all purposes.Generally, ignition of the pyrotechnic charge or other combustiblematerial creates gas pressure in a chamber having a piston to impartmotion upon a driving element such as a piston, rack and pinion, orseries of balls disposed in a pretensioner tube, which engage with andwind a retractor spool sprocket to retract the webbing.

One issue with pretensioners using a series of metallic balls is theweight of the series of balls required for a full pretensioning stroke,as well as the corresponding cost of supplying multiple metallic ballswith strict tolerances. Further, for pretensioners using a series ofmetallic balls, or rack and pinion based systems, is the need for asynchronizing or clutch feature to ensure that the series of balls orpinion sufficiently engage the retractor spool sprocket.

Another issue with pretensioners is known as a low resistance condition,where the driving elements will reach an end of stroke withoutexperience substantial resistance. This can occur if there is excessiveslack in the seatbelt webbing. In these cases, the low resistanceresults in a lower amount of backpressure from the driving elements. Thebackpressure is produced by the engagement between the driving elementsand the sprocket, so lower backpressure reduces the pressure on asealing element that trails the driving elements. Reduced pressure onthe sealing elements reduces the amount that the sealing element iscompressed circumferentially. Reduced sealing ability can cause gas toleak from the tube around the series of balls.

A further issue with pretensioners is the need to maintain the retractorand the seatbelt webbing in a locked condition at the end of thepretensioning stroke. When the retractor spool does not remain locked,payback can occur which allows the seatbelt to unspool and reintroduceslack in the seatbelt. One method for maintaining the locked positionincludes maintaining pressure from the gas generator beyond the amountneeded for the pretensioning stroke. However, this adds weight and cost.

Another issue with pretensioners is the need to vent gas to prevent orin the event of an overpressure condition. This can occur, for example,when the gas generator is deployed and the retractor spool for somereason cannot pretension and the driving elements experience substantialresistance as they attempt to advance toward an end of the pretensioningstroke. This can cause a substantial increase in the pressure ofexpanding gas from the gas generator that is attempting to push thedriving elements.

BRIEF SUMMARY

Seatbelt pretensioning retractor assemblies for use in a passengervehicle are provided herein. In an exemplary embodiment, a seatbeltpretensioning retractor assembly includes a housing that is adapted forbeing mounted to a vehicle structure. The housing has an interiorcavity. A tube has an arcuate and curved shape having a first end forfluid communication with a gas generator and a second end in fluidcommunication with the interior cavity of the housing. A sprocket isrotatably mounted to the housing and is fixedly coupled to a spindleadapted for taking up seatbelt webbing during pretensioning. A drivingelement includes a polymer rod having a proximal end portion that isdisposed towards the gas generator and a distal end portion that isopposite the proximal end portion. The polymer rod is configured toextend in a longitudinal direction from the proximal end portion to thedistal end portion. The polymer rod is disposed within the tube and istranslatable through the tube in a first direction toward the sprocketin response to an actuation by the gas generator. A stopper is coupledto the proximal end portion of the polymer rod. A piston-safety valvemember is disposed between the gas generator and the stopper and isconfigured to allow gas from the gas generator to pass therethrough whenthe gas is at or above a predetermined pressure.

In another exemplary embodiment, a seatbelt pretensioning retractorassembly for use in a passenger vehicle is provided. The seatbeltpretensioning retractor assembly includes a housing adapted for beingmounted to a vehicle structure and has an interior cavity. A tube has anarcuate and curved shape having a first end for fluid communication witha gas generator and a second end in fluid communication with theinterior cavity of the housing. A sprocket is rotatably mounted to thehousing and is fixedly coupled to a spindle adapted for taking upseatbelt webbing during pretensioning. The sprocket has a plurality ofvanes. A driving element includes a polymer rod having a proximal endportion that is disposed towards the gas generator and a distal endportion that is opposite the proximal end portion. The polymer rod isconfigured to extend in a longitudinal direction from the proximal endportion to the distal end portion. The polymer rod is disposed withinthe tube and is translatable through the tube in a first directiontoward the sprocket in response to an actuation by the gas generator. Astopper is coupled to the proximal end portion of the polymer rod. Apiston-safety valve member is disposed adjacent to the stopper on a sideopposite the proximal end portion of the polymer rod. The piston-safetyvalve member includes a piston body and a safety valve operativelycoupled to the piston body. A seal member is disposed between the gasgenerator and the piston-safety valve member and has a through hole influid communication with the safety valve. The seal member and thepiston-safety valve member cooperate to allow gas from the gas generatorto pass therethrough when the gas is at or above a predeterminedpressure.

Further objects, features, and advantages of the invention will becomeapparent to those skilled in the art to which the present inventionrelates from consideration of the following description and the appendedclaims, taken in conjunction with the accompanied drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is perspective view of an occupant restraint system in accordancewith an exemplary embodiment;

FIG. 2 is a perspective view of the occupant restraint system withvarious components removed to show a seatbelt pretensioning retractorassembly in accordance with an exemplary embodiment;

FIG. 3 is a perspective view of the seatbelt pretensioning retractorassembly in accordance with an exemplary embodiment;

FIG. 4 is a cut-away view of the seatbelt pretensioning retractorassembly illustrating a tube, a polymer rod, and a sprocket in anon-actuated position in accordance with an exemplary embodiment;

FIG. 5 is a side cut-away view of the polymer rod and a stopper inaccordance with an exemplary embodiment;

FIG. 6 is a plan view of the sprocket having a plurality of vanes inaccordance with an exemplary embodiment;

FIG. 7 is a side view of the sprocket in accordance with an exemplaryembodiment;

FIG. 8 is a partial view of the sprocket illustrating the shape of thevanes in accordance with an exemplary embodiment;

FIG. 9 is a cross-sectional view of the seatbelt pretensioning retractorassembly in an actuated position in accordance with an exemplaryembodiment;

FIG. 10 is a cross-sectional view of the tube, a seal member, apiston-safety valve member, the stopper, and the polymer rod of theseatbelt pretensioning retractor assembly in accordance with anexemplary embodiment;

FIG. 11 is an exploded side view of the seal member, the piston-safetyvalve member, the stopper, and the polymer rod in accordance with anexemplary embodiment;

FIG. 12 is a cross-sectional view of the piston-safety valve member inaccordance with an exemplary embodiment;

FIG. 13 is an exploded perspective side view of the piston-safety valvemember in accordance with an exemplary embodiment;

FIG. 14 is a partial exploded perspective view of the tube, the polymerrod, and the stopper in accordance with an exemplary embodiment;

FIGS. 15A-15C are cross-sectional views of various embodiments of thetube and the stopper illustrated in FIG. 10 along line 15-15;

FIGS. 16A-16E are cross-sectional views of various embodiments of thepolymer rod illustrated in FIG. 5 along line 16-16;

FIG. 17 is a cross-sectional view of an embodiment of a constrictionportion in the tube;

FIG. 18 is a cross-sectional view of another embodiment of theconstriction portion;

FIG. 19 is a cross-sectional view of another embodiment of theconstriction portion;

FIGS. 20A and 20B are perspective views of the polymer rod in accordancewith an exemplary embodiment; and

FIGS. 21A-21D are cross-sectional views of the piston-safety valvemember, the stopper, and the proximal section of the polymer rod inaccordance with various exemplary embodiments.

It should be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features.

DETAILED DESCRIPTION OF THE INVENTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure or its application or uses.

Referring now to the drawings, FIG. 1 shows a vehicle seat 10 and aseatbelt assembly 12 in accordance with an exemplary embodiment. Theseatbelt assembly 12 includes a seatbelt webbing 14 having a shoulderbelt portion 16 extending from an upper guide loop or anchorage 18 to alatch plate 20 and a lap belt portion 22 extending from the latch plate20 to an anchorage 24. The latch plate 20 can include a loop portion 26through which the seatbelt webbing 14 extends. The latch plate 20 isable to be inserted into a seatbelt buckle 28 to lock and unlock theseatbelt assembly 12. A seatbelt buckle cable 30, either directly or incooperation with other components, secures the seatbelt buckle 28 to aportion 31 of the vehicle structure (e.g., vehicle frame). It will beappreciated that other manners of attaching the seatbelt webbing 14 tovehicle could also be used, including variations on the latch plate 20and the seatbelt buckle 28 and their attachments to the seatbelt webbing14 and associated vehicle structure.

The seatbelt webbing 14 is able to pay-out from a seatbelt pretensioningretractor assembly or retractor assembly 32 (shown in FIGS. 2 and 3),which is located within the vehicle seat 10 (in an integrated structuralseat design) or is coupled structurally to the vehicle body, so that theeffective length of the seatbelt webbing 14 is adjustable. When thelatch plate 20 has been fastened to the seatbelt buckle 28, the seatbeltassembly 12 defines a three-point restraint between the anchorage 18,the latch plate 20, and the anchorage 24. Any other suitableconfigurations, such as alternative locations for the retractor assembly32, the latch plate 20, and the anchorage 24, may be used with thepresent invention.

Now with reference to FIG. 2, an isometric view of the seatbelt assembly12 is illustrated disassociated from the motor vehicle and showing theretractor assembly 32 in accordance with an exemplary embodiment. Theretractor assembly 32 includes a spool assembly 34 and a gas generator36 mounted to a common frame 38. The spool assembly 34 is connected withand stows the seatbelt webbing 14 of the shoulder belt portion 16,whereas the end of the lap belt portion 22 of the seatbelt webbing 14 isfixedly engaged with the anchorage point, for example, the frame 38 oranother portion of the motor vehicle such as the seat 10 (shown inFIG. 1) or floor pan.

Referring also to FIG. 3, the spool assembly 34 includes a belt spool 40that engages the shoulder belt portion 16 of the seatbelt webbing 14 androtates to wind-up or pay-out the seatbelt webbing 14. A torsional“clock” or “motor” type spring is carried within a spring end cap 42 androtationally biases the belt spool 40 to retract the seatbelt webbing14. The spool assembly 34 may further incorporate other spool controlmechanisms that are known in accordance with the prior art, includingpretensioners, inertia and webbing sensitive locking devices, torsionbar load limiters, or other belt control devices. “Spool controlsystems” referred to in this specification may include any system thatcontrols the rotational movement of a webbing spool, thus controllingthe extraction and retraction of seatbelt webbing. One such spoolcontrol system is a motor-assisted retractor. Spool locking devicestypically incorporate an inertia sensitive element, such as a rollingball or pendulum, and cause a sprocket of the spool to be engaged toprevent further withdrawing of the seatbelt webbing 14 from the beltspool 40. Webbing sensitive locking devices sense rapid pay-out ofseatbelt webbing 14 to lock the retractor assembly 32. Variouselectronic sensing mechanisms that detect the withdrawal of seatbeltwebbing 14 and/or the connection of the latch plate 20 to the seatbeltbuckle 28 may also be incorporated into the retractor assembly 32.

During normal operation of the vehicle, the retractor assembly 32 allowspay-out of seatbelt webbing 14 to give the occupant a certain amount offreedom of movement. However, if an impact or a potential impactsituation is detected, the retractor assembly 32 is locked to preventpay-out and to secure the occupant in the seat 10. For example, if thevehicle decelerates at a predetermined rate or if the brakes areactuated with a predetermined force, then the retractor assembly 32 islocked. Due in part to the free pay-out of the seatbelt webbing 14, theseatbelt assembly 12 often develops slack during normal use.

FIG. 4 provides a cut-away illustration of a pretensioner system 44 inaccordance with an exemplary embodiment. Referring to FIGS. 3-4, inparticular, the retractor assembly 32 further incorporates thepretensioner system 44 operatively connected to the spool assembly 34and operable to rotate the belt spool 40 for pretensioning. As known tothose of skill in the art, a retractor pretensioner winds seatbeltwebbing into a more taught condition against the occupant at the initialstages of a detected vehicle impact. This is provided to reduce forwardmotion or excursion of the occupant in response to the decelerationforces of a vehicle impact or rollover.

The pretensioner system 44 includes a pretensioner tube 52 incommunication with the gas generator 36. The gas generator 36 is used toprovide expanding gas in response to a firing signal. As is known in theart, for example, the vehicle includes a sensor array sending a signalindicative of an emergency event such as an impact event, crash, orrollover. The vehicle sensor may be a specific impact sensor, or may bea traditional vehicle sensor (e.g. a longitudinal or lateralacceleration sensor) or otherwise part of a control system having asuite of multiple sensors. Any other impact sensor that is or will beknown to those skilled in the art may also be readily employed inconjunction with the seatbelt assembly 12 of present invention. Anelectronic control unit such as a central processing unit (CPU) or othercontroller receives a signal and controls the seatbelt assembly 12 torespond by tightening the seatbelt webbing 14 of the vehicle (e.g. viaactivation of a pretensioner).

As will be discussed in further detail below, the pretensioner tube 52has a pretensioner rod 53, e.g., a polymer rod or a plasticallydeformable polymer rod, disposed therein that has an elongate shape andis flexible within the tube 52. More specifically and as will bediscussed in further detail below, the pretensioner rod 53, whendisposed outside of the pretensioner tube 52 prior to insertion therein,has a generally straight shape, and when inserted into the tube 52 itwill bend and flex in accordance with the tortuous shape of the tube 52.

Turning now to the retractor assembly 32, the retractor assembly 32includes the spool assembly 34 mounted to the common frame 38, asdescribed above. More particularly, the spool assembly 34 will rotaterelative to the common frame 38 to wind the seatbelt webbing 14 attachedto the spool assembly 34. The common frame 38 includes a housing 54 forhousing the components of the pretensioner system 44.

The spool assembly 34 includes a sprocket 56 that is disposed within thehousing 54. The sprocket 56 is attached to the belt spool 40. Rotationof the sprocket 56 will cause the attached belt spool 40 to rotate towind the seatbelt webbing 14 that is attached to the belt spool 40.

FIG. 5 provides a side cut-away illustration of the pretensioner rod 53and a stopper 55 in accordance with an exemplary embodiment. FIGS.16A-16E provide cross-sectional views of various embodiments of thepretensioner rod 53 illustrated in FIG. 5 along line 16-16. As shown inFIGS. 5 and 16A-16E, the pretensioner rod 53 has a generally circularcross-section in one form. In another approach, the pretensioner rod 53could have a non-circular cross-section, such as a generally rectangularcross-section, generally triangular cross-section, or other polygonalcross-section that allows the pretensioner rod 53 to be inserted intothe pretensioner tube 52 (shown in FIG. 4) and adapt to the tortuousshape of the pretensioner tube 52 when inserted. For purposes ofdiscussion, the pretensioner rod 53 will be discussed as having agenerally circular cross-section

As illustrated and as discussed above, the pretensioner rod 53, whendisposed outside of the pretensioner tube 52, has a generally straightshape and extends in a longitudinal direction 200 from a proximal endportion 202 to a distal end portion 204. The proximal end portion 202 isdisposed towards the gas generator 36 (shown in FIG. 10) when thepretensioner rod 53 is installed within the pretensioner system 44. Inan exemplary embodiment, the pretensioner tube 52 has a cross-sectionthat varies along its length to define a non-recessed portion 206 and arecessed portion 208 that defines a recess 210. In one example and asillustrated in FIGS. 5 and 16D, the recess 210 is configured as a groove212, e.g., U-shaped groove with sidewalls 214 a. In another example andas illustrated in FIG. 16A, the recessed portion 208 has a recessedruled surface 214 b, e.g., substantially flat surface, which defines therecess 210. Non-limiting alternative examples of different forms of therecess 210 are illustrated in FIGS. 16B-16C and 16E.

Referring to FIG. 5, in an exemplary embodiment, the recessed portion208 extends along a majority of the overall length of the pretensionerrod 53 from the proximal end portion 202 to and including the distal endportion 204. As illustrated, the proximal end portion 202 includes thenon-recessed portion 206 in which the recess 210 terminates at adistal-most section of the non-recessed portion 206. As will bediscussed in further detail below and as illustrated in FIGS. 5 and16A-16E, the non-recessed portion 206 of the pretensioner rod 53 has adiameter, cross-sectional dimension, and/or perimeter greater than therecessed portion 208. In an exemplary embodiment, the non-recessedportion 206 has a length L1 of from about 15 to about 25 mm, such asabout 20 mm and a width W1 of from about 4 to about 7 mm, and therecessed portion 208 has a length L2 of from about 60 to about 145 mmand a thickness W2 of from about 2.5 to about 8.0 mm.

In an exemplary embodiment, the pretensioner rod 53 also includes apositive feature 216, e.g., nub or post, extending proximally from theproximal end portion 202. The stopper 55 has a negative feature 218formed therein that receives the positive feature 216 to couple thestopper 55 to the proximal end portion 202 of the pretensioner rod 53.In one example, the negative feature 218 and the positive feature 216are sized such that the stopper 55 is compression fit, e.g.,interference fit, onto the positive feature 216 to fixedly couple thestopper 55 to the pretensioner rod 53. Other forms of coupling and/orfixing the stopper 55 to the positive feature 216 and/or the proximalend portion 202 may be used, such as, for example, an adhesive,mechanical means, or the like. As illustrated in FIG. 5, the negativefeature 218 can be configured as a blind hole 220.

In an exemplary embodiment, the pretensioner rod 53 is made from apolymer material, which has a reduced weight relative to metallic balldriving elements of other roto-pretensioners. The particular polymermaterial can be selected to fit the particular desires of the user. Thepolymer material is preferably one that has sufficient flexibility suchthat it can bend and flex through the pretensioner tube 52 to allow forinitial installation as well as in response to actuation by the gasgenerator 36. The polymer material is preferably one that has sufficientpushability in response to actuation, such that the pretensioner rod 53will sufficiently transfer a load to a sprocket 56 of the pretensionersystem 44, thereby functioning as a driving element for causingpretensioning.

Further, in an exemplary embodiment, the pretensioner rod 53 is madefrom a polymer material that is plastically deformable. During and afteractuation, the pretensioner rod 53 will be become plastically deformedin response to actuation and contact with other components (e.g., thesprocket 56) of the pretensioner system 44. As will be discussed infurther detail below, this plastic deformation will cause thepretensioner rod 53 to become locked, for example, in the sprocket 56 toprevent or limit payback of the pretensioner rod 53 without beingcompletely dependent on maintained pressure in the system.

In one approach, the pretensioner rod 53 is made from a nylonthermoplastic material. The pretensioner rod 53 could also be made froman aliphatic polyamide thermoplastic material. In another approach, thepretensioner rod 53 could be made from a similar thermoplastic material,such as an acetal material or polypropylene material.

With reference to FIGS. 6-8, the sprocket 56 has a general annular shapethat defines an internal aperture 76. The sprocket 56 further defines aplurality of inward extending teeth 78 that extend into the aperture 76.The teeth 78 are sized and configured to correspond to recesses ordepressions that are defined on an external surface of the belt spool 40(shown in FIG. 3) to connect the sprocket 56 to the belt spool 40 suchthat they are rotationally coupled. In another approach, the internalaperture 76 could include a single tooth or protrusion to rotationallycouple the sprocket 56 to the belt spool 40.

The sprocket 56 includes an annular body portion 80 and a flange portion82 that projects radially from the base of the annular body portion 80.The sprocket 56 further includes a plurality of vanes 84 that eachproject radially from the annular body portion 80 as well aslongitudinally from the flange portion 82, such that vanes 82 extendbetween the annular body portion 80 and the flange portion 82.

The vanes 84 each have a generally triangular shape when viewed from thefront, with a base that tapers into a point 86 as the vane 84 extendsradially outward from the annular body portion 80. The particular widthand pitch of the vanes 84 can be selected as desired. The plurality ofvanes 84 combine to define cavities 88 that are disposed betweenadjacent vanes 84.

In one approach, each of the vanes 84 can have the same size and shapeand be uniformly distributed around the sprocket 56. In anotherapproach, the vanes 84 can have different sizes and/or be spaced atdifferent intervals. Adjusting the size and spacing of the vanes 84 canalter the amount of rotation and/or the rate of the rotation for thesprocket 84 when the pretensioner system 44 is activated. This variablesize and/or spacing is possible due to the actuation by the pretensionerrod 53 rather than by a series of similarly shaped balls. In apretensioner that uses a plurality of ball-shaped driving elements, thesize and spacing is preferably uniform to account for the predeterminedshape and size of the balls.

With reference once again to FIG. 4, the housing 54 further include aguide portion 90. The guide portion 90 is disposed within the housing 54similar to the sprocket 56. More particularly, the guide portion 90 isdisposed opposite an exit 89 of the tube 52, and the sprocket 56 isdisposed between the guide portion 90 and the tube 52. Accordingly, thepretensioner rod 53 exiting the tube 52 will contact the sprocket 56prior to contacting the guide portion 90.

The guide 90 has a generally arcuate landing surface 92 that has aconcave shape toward the exit of the tube 52. In one approach, the arcof the surface 92 has a constant radius. Further, the center point ofthe radius of the arc is aligned with the rotational axis of thesprocket 56, such that the radial spacing between the surface 92 and thesprocket 56 is consistent along the length of the surface 92. In anotherapproach, the center point of the radius of the surface 92 could beoffset from sprocket axis, such that the radial spacing between thesurface 92 and the outer diameter of the sprocket 56 will vary atdifferent points along the surface 92.

The surface 92 includes a first end 96 and second end 98. The first end96 is disposed opposite the exit 89 of the tube 52 such that thepretensioner rod 53 would engage the first end 96 prior to the secondend 98 after exiting the tube 52 and passing the sprocket 56.

The housing 54 further defines an overflow cavity 100 that is disposedopposite the guide 90. The overflow cavity 100 is also disposed adjacentthe curvature of the tube 52, and the sprocket 56 is disposed betweenthe guide 90 and the overflow cavity 100. Accordingly, an intermediateportion 101 of the guide 90 is diametrically opposite the overflowcavity 100 across the sprocket 56.

The overflow cavity 100 is sized and configured to allow a portion thepretensioner rod 53 to be received therein during actuation ofpretensioner system 44, if necessary. For example, after thepretensioner rod 53 has exited the tube 52 it will contact the guide 90and be directed in an arcuate path corresponding to the guide 90, suchthat the pretensioner rod 53 is ultimately directed toward the overflowcavity 100. The pretensioner rod 53 can extend into the overflow cavity100, and can further be guided along the curvature of the tube 52 thatis adjacent the overflow cavity 100. However, it will be appreciatedthat the pretensioner rod 53 may not necessarily travel far enoughduring actuation to ultimately reach the overflow cavity 100.

As described above, the retractor assembly 32 includes the gas generator36 that provides expanding gas in response to a firing signal. Theexpanding gas causes an increase in pressure within the tube 52, whichultimately causes the pretensioner rod 53 to be forced away from the gasgenerator 36, through the tube 52, and pass the exit 89 into thesprocket 56 for pretensioning.

More particularly, as shown in FIGS. 10-11, the pretensioner tube 52includes piston-safety valve member 300 that is disposed adjacent to thestopper 55 opposite the pretensioner rod 53, and a seal member 102 thatis disposed between the gas generator 36 and the piston-safety valvemember 300. In an exemplary embodiment, the piston-safety valve member300 and the seal member 102 are operatively coupled together andslidably disposed within the tube 52 to function as a piston duringpretensioning to drive the pretensioner rod 53 along an actuatingdirection or path A through the tube 52 and into the sprocket 56. Aswill be discussed in further detail below, to prevent or in the event ofan overpressure condition during pretensioning, however, thepiston-safety valve member 300 and the seal member 102 cooperate toallow gas from the gas generator 36 to pass therethrough when the gas isat or above a predetermined pressure. It should be noted however thatalthough the various embodiments disclosed herein described the sealmember 102 and the piston-safety valve member 300 cooperating tofunction as a piston, it is to be appreciated by those skilled in theart that it is within the scope of the present disclosure that thepiston-safety valve member 300 may function independently as a pistonwithout the seal member 102, for example, by modifying the piston-safetyvalve member 300 to additionally provide a sealing feature with theinterior wall of the tube 52. For example, the piston-safety valvemember 300 may be formed of a relatively flexible material that maycircumferentially expand against the interior wall of the tube 52 duringpretensioning due to pressure from the gas from the gas generator 36,and/or the outer surface of the piston-safety valve member 300 may bedesigned to be near a net fit with the interior wall of the tube 52 tosubstantially prevent the gas from advancing past the piston-safetyvalve member 300 between the outer surface of the member 300 and theinterior wall of the tube 52.

Referring to FIGS. 10-13, in an exemplary embodiment, the piston-safetyvalve member 300 includes a piston body 302 and a safety valve 304operatively coupled to the piston body. In one example, the diameter ordimensions that define the outer surface of the piston body 302, whichmay be cylindrical in shape or otherwise, are sized slightly smallerthan the width of the tube 52 to facilitate the piston-safety valvemember 300 translating through the tube 52.

The safety valve 304 includes a safety valve diaphragm 306 and a lipinsert 308 that interfaces with the stopper 55. The safety valvediaphragm 306 is disposed between the piston body 302 and the lip insert308. In particular, the piston body 302 has a wall 309 that defines abody opening 310 (e.g., a through hole) and that includes a step orshoulder portion 311 at least partially surrounding the body opening311. The body opening 310 is in fluid communication with the safetyvalve diaphragm 306.

Likewise, the lip insert 308 has a lip insert opening 312 (e.g., athrough hole) formed therethrough that is in fluid communication withthe safety valve diaphragm 306 on a side opposite the body opening 310.As illustrated, the safety valve diaphragm 306 is “cup-shaped” with asidewall 314 that surrounds a central diaphragm portion 316. The safetyvalve diaphragm 306 is disposed between the shoulder portion 311 of thepiston body 302 and the lip insert 308 with the sidewall 314 disposed onthe shoulder portion 311 and the central diaphragm portion 316 extendingacross the body opening 310. As such, when fully intact, the centraldiaphragm portion 316 of the safety valve diaphragm 306 provides a sealor otherwise obstructs fluid communication between the body opening 310and the insert opening 312. As will be discussed in further detailbelow, to prevent or in the event of an overpressure condition, thecentral diaphragm portion 316 of the safety valve diaphragm 306 rupturesat a predetermined pressure, thereby breaking the seal to allow fluidcommunication from the body opening 310 to the insert opening 312.

As illustrated, the lip insert 308 has a lip portion 318 that contactsthe stopper 55 along an interface 320. The lip insert 308 has channelsthat are formed along the lip portion 318 that allow fluid (e.g., gasfrom the gas generator 36) to advance from the lip insert 308 (e.g., theinsert opening 312) downstream past the interface 320 and along theexterior of the stopper 55.

In an exemplary embodiment, the seal member 102 sealingly interfaceswith the piston-safety valve member 300 and has a through hole 324 influid communication with the safety valve 304. As such, duringpretensioning, gas from the gas generator 36 can pass through thethrough hole 324 of the seal member 102 and the body opening 310 to thesafety valve diaphragm 306 of the piston-safety valve member 300. Asdiscussed above, when the central diaphragm portion 316 of the safetyvalve diaphragm 306 is intact (e.g., during normal pretensioningconditions below the predetermined pressure for rupturing the centraldiaphragm portion 316), gas from the gas generator 36 will besubstantially obstructed from advancing further downstream to help pushthe pretensioner rod 53 through the tube 52.

The seal member 102 can have a generally cylindrical shape with agenerally cylindrical outer surface, in one approach. In anotherapproach, the seal member 102 can have a spherical shape with aspherical outer surface, or another appropriate shape and outer surfacefor sealing. As will be understood by those of skill in the art, theseal member 102 may be press-fitted or otherwise fitted inside the tube52.

As shown in FIG. 10, the seal member 102 has a proximal end spaced fromthe gas generator 36 so as to define a gas chamber therebetween. Theseal member 102 has a distal end that sealingly interfaces with thepiston-safety valve member 300 and that is directed toward the stopper55 and the pretensioner rod 53.

The stopper 55 is preferably made from aluminum, but could be made fromanother suitable material of sufficient strength, such as steel, othermetal or metal alloy, or reinforced plastic. In an exemplary embodiment,the stopper 55 has an outer perimeter that substantially matches theperimeter of the non-recessed portion 206. The stopper 55 is adjacentthe distal end of the piston-safety valve member 300 interfacing withthe lip portion 318 of the member 300 along the interface 320. In anexemplary embodiment, the stopper 55 has an outer surface 326 that iscurved and that interfaces with the lip portion 316. In one example andas illustrated, the outer surface 326 of the stopper 55 is configured asa semi-hemispherical surface.

Referring also to FIGS. 15A-15C, in an exemplary embodiment, a gap 328is provided between the stopper 55 and an inner surface 330 of the tube52. As will be discussed in further detail below, to prevent or in theevent of an overpressure condition, fluid (e.g., gas from the gasgenerator 36) flowing downstream past the interface 320 of the lipportion 318 of the piston-safety valve member 300 and the stopper 55 cancontinue to flow downstream through the gap 328 and past the stopper 55.In one example and as illustrated in FIG. 15B, the outer surface 326 ofthe stopper 55 has notches 332 that form at least part of the gap 328between the stopper 55 and the inner surface 330 of the tube 52. Inanother example and as illustrated in FIG. 15A, at least a portion ofthe outer surface 326 of the stopper 55 is substantially noncircular andthe inner surface 330 of the tube 52 is substantially circular so as toform at least part of the gap 328 between the stopper 55 and the innersurface 330 of the tube 52. In another example and as illustrated inFIG. 15C, at least a portion of the outer surface 326 of the stopper 55is substantially circular and the inner surface 330 of the tube 52 issubstantially circular but having a larger diameter than the outersurface 326 of the stopper 55 to form the gap 328 between the stopper 55and the inner surface 330 of the tube 52.

During pretensioning, the seal member 102, the piston-safety valvemember 300, and the stopper 55 cooperate to transfer the energy from theincreased pressure in the gas chamber 108 to the pretensioner rod 53.The pretensioner rod 53, in order to travel through the tube 52 and flexaccording to the curvature of the tube 52, is sized slightly smallerthan the width of the tube 52. Thus, without the seal member 102 and thepiston-safety valve member 300, gas from the gas generator 36 would flowpast the pretensioner rod 53 in the space defined between thepretensioner rod 53 and the tube 52.

The seal member 102 defines a generally elastic structure, and may becomposed of various materials known in the art, such as any suitableplastic or polymer (e.g., silicone, polyester, rubber, thermoplastic, orother elastic or deformable material). In an exemplary embodiment, theseal member 102 is made from silicone. Moreover, the seal member 102 maybe die cast, forged, or molded from metal, plastic, or other suitablematerial. In one embodiment, the seal member 102 is formed using atwo-cavity injection molding process. The generally elastic structureallows the shape of the seal member 102 to change slightly in responseto pressure, thereby improving the sealing that it provides.

Referring to FIGS. 9-10, in operation, the gas generator 36 producesexpanding gas that pressurizes the gas chamber, thereby enabling theseal member 102 and the piston-safety valve member 300 to forcibly drivethe pretensioner rod 53 along the actuation path A. As the pretensionerrod 53 is driven through the tube 52, it engages the sprocket 56. Moreparticularly, the pretensioner rod 53 engages the vanes 84 of thesprocket 56. Engagement of the pretensioner rod 53 with the sprocket 56as the pretensioner rod 53 is driven by expanding gas in the directionof arrow A causes the belt spool 40 (shown in FIG. 3) to rotate, whichin turn provides pretensioning.

Activation of the gas generator 36 enables the seal member 102 sealinglyinterfacing with the piston-safety valve member 300 to resist gasleakage. As previously mentioned, the seal member 102 is composed of arelatively elastic material. Therefore, pressurized gas within the gaschamber 108 causes the seal member 102 to expand, which helps preventgas from escaping past the seal member 102 and the piston-safety valvemember 300.

In addition, backpressure generated from the pretensioner rod 53 causesthe seal member 102 to expand circumferentially outward due tocompression of the seal member 102 against the piston-safety valvemember 300, the stopper 55, and the pretensioner rod 53. Thepretensioner rod 53 undergoes resistance as it engages the sprocket 56during actuation, thereby generating backpressure on the stopper 55,piston-safety valve member 300, and the seal member 102. Thecircumferential expansion of the seal member 102 provides a tightenedseal between the outer surface of the seal member 102 and the inner wallof the pretensioner tube 52. Accordingly, the seal member 102 with thepiston-safety valve member 300 of the present invention is operable toretain a high seal pressure as well as maintain residual gas pressurewithin the tube 52.

During pretensioning of the seatbelt there can be a side-effect known aspayback, where the tension on the seatbelt caused by the occupant duringan event triggering pretensioning can rotate the spool in a directionopposite the pretensioning rotation. This rotation is transferred to thesprocket 56 and the driving elements, causing the driving elements totravel in the reverse direction within the tube 52. Payback can becounteracted by maintaining pressure in the tube 52, but this requiresthe gas generator 36 to fire for a longer period and additionalpropellant.

However, in an exemplary embodiment, the pretensioner system 44described herein includes features configured to counteract the abovedescribed payback side-effect as an alternative to or in addition tomaintained gas pressure. As described above, the pretensioner rod 53 ispreferably made of a plastically deformable material, such as a polymer.

During actuation of the pretensioner system 44, the pretensioner rod 53exits the tube 52 and contacts the vanes 84 of the sprocket 56, causingthe sprocket 56 to rotate. As the pretensioner rod 53 continues past thesprocket 56 causing it to rotate, additional ones of vanes 84 willcontact the side of the pretensioner rod 53, causing the pretensionerrod 53 to be compressed and deformed plastically in the area ofinterference between the vanes 84 and the pretensioner rod 53. Thiscompression will also cause the pretensioner rod 53 to be compressedagainst the guide 90, creating a press-fit configuration of thepretensioner rod 53 between the sprocket 56 and the guide 90.

Additionally, the pretensioner rod 53 and guide 90 may be made frommaterials that will weld together at the end of the pretensioningstroke. For example, the materials of the pretensioner rod 53 and guide90 may be selected such that heat generated from the friction betweenthe pretensioner rod 53 and the guide 90 will cause the pretensioner rod53 and guide 90 to become welded together along an interface W where theguide 90 and rod 53 contact each other. Once the pretensioner rod 53 andguide 90 are welded together, the pretensioner rod 53 will become lockedand prevented or substantially limited from traveling back into the tube52. The plastic deformation of the pretensioner rod 53 caused by thevanes 84 will prevent or substantially limit the sprocket 56 fromrotating in the opposite direction, thereby preventing or substantiallylimiting payback.

The welding results from the relatively high heat and pressure generatedby the system during actuation. For the pretensioner rod 53 and guide 90to weld, the materials used for each are preferably in the same family.For example, if the guide 90 is nylon, then the pretensioner rod 53 ispreferably nylon. Similarly, if the guide 90 is acetal, then thepretensioner rod 53 is preferably acetal. If the guide 90 ispolypropylene, then the pretensioner rod 53 is polypropylene. It will beappreciated that other materials that will weld together under high heatand pressure could also be used. Moreover, it will be appreciated thatsome different types of materials can weld together.

Another side-effect that can occur during pretensioning is known as alow-resistance condition. This can occur when there is a relativelylarge portion of the seatbelt webbing that can be taken up or wound bythe spool in response to actuating the pretensioner. For example, ifthere was extra slack in the seatbelt, this slack would be taken up andwound with lower resistance because it would not be acting on theoccupant until the slack was taken up. In a low resistance condition,the backpressure of the driving elements is reduced. Reducedbackpressure can result in a reduced ability of the sealing element toexpand circumferentially against the inner wall surface of the tube inresponse to the backpressure. This can occur for any type of piston orseal that is configured to expand circumferentially in response tobackpressure as part of its sealing process.

With reference to FIGS. 4, 9-10, and 14, to address the side-effect of alow-resistance condition of the pretensioner system 44, in an exemplaryembodiment, the tube 52 includes a projection 120 extending within thetube 52 near an end (e.g., exit 89) of the tube 52 to form constrictionportion 130 proximate to where the pretensioner rod 53 exits, therebyreducing the cross-sectional area of the tube 52 in a distinct location.That is, the opening diameter, width, or dimension(s) of theconstriction portion 130 is smaller than the diameter, width, ordimension(s) of adjacent portions of the tube 52 portions, such as, forexample, the portions of the tube 52 that are upstream from theconstriction portion 130.

As will be discussed in further detail below, the recess 210 of thepretensioner rod 53 is aligned with the projection 120 along theactuating direction or path A such that during actuation and/orpretensioning, the recessed portion 208 of the pretensioner rod 53 isnot obstructed by the projection 120. Moreover, the constriction portion130 is sized such that there is enough space that at least the recessedportion 208 of the pretensioner rod 53 can travel past the constrictionportion 130, but the stopper 55, the piston-safety valve member 300, andseal member 102 will be blocked from travelling past the constrictionportion 130. When the stopper 55, piston-safety valve member 300, andthe seal member 102 are blocked from advancing past the constrictionportion 130, the constriction portion 130 provides additionalbackpressure. Accordingly, the seal member 102 will circumferentially orradially expand in response to this backpressure, thereby providing animproved seal in low-resistance conditions. This improved sealing willprevent or limit the potential for gas to escape from the tube 52 inlow-resistance conditions.

The projection 120 defining the constriction portion 130 can be formedin a variety of ways and have a variety of shapes while providing theabove described functionality. In one approach, shown in FIGS. 4, 9, and14, the projection 120 is in the form of a crimp or bump 132 in the tube52, such that the sidewall of the tube 52 maintains substantially thesame thickness. The bump 132 is integrally formed with the tube as amonolithic structure, at least in the area of the constriction portion130. Put another way, the bump 132 is not a separate component ormaterial attached to the tube 52. The bump 132 protrudes into the tube52, and has a corresponding depression on an outer surface of the tube52. The bump 132 has a convex shape within the tube 52 and thedepression has a corresponding concave shape.

In another approach, shown in FIG. 17, the projection 120 could be inthe form of an increased thickness portion 138 that is integral with thetube 52. This is similar to the bump 132, but does not have acorresponding depression on outer surface of the tube 52.

In another approach, shown in FIG. 18, the projection 120 is in the forma separate piece or crescent 136 that is attached to the tube 52 withinthe tube 52. The crescent 136 a, 136 b, or 136 c can be attached viawelding, adhesive, mechanical fasteners, or the like.

In another approach, shown in FIG. 19, the projection 120 could be inthe form of a plate 140 that is inserted through an opening 142 formedin the sidewall of the tube 52. The plate 140 is removably insertedthrough the opening 142 and secured to the tube 52 via known securementmechanisms. In another approach, the plate 140 can be fixedly securedafter insertion through the opening 142. The use of the plate 140 allowsfor different shapes and sizes and materials to be easily selected andinstalled, if desired.

In the above approaches, the projection 120 with the recess 210 of thepretensioner rod 53 aligned therewith may be disposed along an inboardportion of the tube 52 as illustrated in solid lines in FIGS. 4 and 9,or alternatively, may be disposed along an outboard portion of the tube52 as illustrated in FIG. 14 and in dashed lines in FIGS. 4 and 9.Advantageously, in an exemplary embodiment, disposition of theprojection 120 on the outboard portion of the tube 52 facilitatesdirecting the distal end portion 204 of the pretensioner rod 53 awayfrom the outboard portion of the tube 52 into engagement with the vanes84 of the sprocket 56, thereby engaging the fully or solid side of thepretensioner rod 53 (e.g., sprocket 56 engaging side of the pretensionerrod 53 opposite the recess 210) during actuation. This can help to lockthe pretensioner rod 53 with the sprocket 56 to prevent or reduce anytranslation of the pretensioner rod 53 in a direction opposite theactuating direction or path A. Alternatively, the projection 120 withthe recess 210 of the pretensioner rod 53 aligned therewith may bedisposed along an inboard portion, or any other side portion, of thetube 52.

As described above, the pretensioner rod 53 has the non-recessed portion206 at its proximal end portion 202, where the non-recessed portion 206has a larger diameter or cross-sectional dimension(s) than the recessedportion 208. In one approach, the non-recessed portion 206 has adiameter or cross-sectional dimension(s) that is larger than the widthor cross-sectional dimension(s) of the tube 52 at the constrictionportion 130. Accordingly, with the non-recessed portion 206 disposedupstream of the constriction portion 130, the constriction portion 130will prevent the non-recessed portion 206 from passing.

In another approach, the non-recessed portion 206 can be smaller thanthe width or cross-sectional dimension(s) of the tube 52 at theconstriction portion 130. With the non-recessed portion 206 being smallenough to pass the constriction potion 130, it can pass beyond theconstriction portion 130.

Another side-effect that can occur during pretensioning is known as anoverpressure condition. This can occur, for example, when the retractorbelt spool for some reason cannot pretension and the driving elementsexperience substantial resistance as they attempt to advance toward anend of the pretensioning stroke. This can cause a substantial increasein the pressure of the gas from the gas generator 36 that is advancingto expand and push the driving elements.

With reference to FIGS. 9-13, to address the side-effect(s) of anoverpressure condition of the pretensioner system 44, in an exemplaryembodiment, the tube 52 includes the sealing member 102 and thepiston-safety valve member 300 to help vent gas to prevent or in theevent of an overpressure condition as discussed above. In particular,when gas from the gas generator 36 is at or above a predeterminedpressure that is associated with an overpressure condition, the sealingmember 102 expands circumferentially outward due to compression of theseal member 102 against the piston-safety valve member 300. However, gasfrom the gas generator 36 can still pass through the through hole 324 ofthe seal member 102 and the body opening 310 of the piston body 302 toapply pressure to the safety valve diaphragm 306. Due to the excessivepressure of the gas at or above the predetermined pressure, the centraldiaphragm portion 316 of the piston-safety valve member 300 isconfigured to rupture (e.g., via thickness and choice of materials usedto form the diaphragm) to allow the gas to flow therethrough downstreamthrough the insert opening 312 in the channels 322 of the lip insert308, and passed the stopper 55 through the gap(s) 328. The gas cancontinue to flow downstream between the spaces between the outer surfaceof the pretensioner rod 53 and the interior wall of the tube 52 and/oralong the recess 210 of the pretensioner rod 53 to be vented through theexit 89 of the tube 52, or alternatively through the tube vent opening400 that may be optionally formed through the tube 52 proximate the exit89 and/or the projection 120. As such, gas from the gas generator 36 canbe vented to address, mitigate, and/or prevent an overpressurecondition.

Referring to FIGS. 20A-21D, alternative embodiments for the pretensionerrod 53, the piston-safety valve member 300, and the stopper 55 areprovided. As illustrated, the recessed portion 208 of the pretensionerrod 53 may extend to the proximal-most end of the pretensioner rod 53immediately adjacent to the stopper 55. As such, there is fluidcommunication between the stopper 55 and the pretensioner rod 53 alongthe recessed portion 208. Additionally, non-limiting alternativeconfigurations for the piston-safety valve member 300 are illustrated inFIGS. 21A-21D in which the safety valve diaphragm 306 is mounted in thepiston body 302 and the piston-safety valve member 300 is mounteddirectly on the stopper 55, for example, without the lip insert 308. Asillustrated, the safety valve diaphragm 306 is disposed between thepiston body of the piston-safety valve member 300 and the stopper 55. Inthese non-limiting alternative configurations, gas from the gasgenerator 36 passes through the through hole of the seal member 102 andthe body opening of the piston body 302 to apply pressure to the safetyvalve diaphragm 306. Due to the excessive pressure of the gas at orabove the predetermined pressure, the safety valve diaphragm 306ruptures to allow the gas to flow downstream into and through therecessed portion 208 of the pretensioner rod 53 to be vented through theexit 89 of the tube 52, or alternatively through the tube vent opening400. As such, gas from the gas generator 36 can be vented to address,mitigate, and/or prevent an overpressure condition.

As a person skilled in the art will readily appreciate, the abovedescription is meant as an illustration of the implementation of theprinciples of this invention. This description is not intended to limitthe scope or application of this invention in that the invention issusceptible to modification, variation, and change, without departingfrom the spirit of this invention as defined in the following claims.

1. A seatbelt pretensioning retractor assembly for use in a passengervehicle, the seatbelt pretensioning retractor assembly comprising: ahousing adapted for being mounted to a vehicle structure and having aninterior cavity; a tube having an arcuate and curved shape having afirst end for fluid communication with a gas generator and a second endin fluid communication with the interior cavity of the housing; asprocket rotatably mounted to the housing and fixedly coupled to aspindle adapted for taking up seatbelt webbing during pretensioning; adriving element comprising a polymer rod having a proximal end portionthat is disposed towards the gas generator and a distal end portion thatis opposite the proximal end portion, and is configured to extend in alongitudinal direction from the proximal end portion to the distal endportion, wherein the polymer rod is disposed within the tube and istranslatable through the tube in a first direction toward the sprocketin response to an actuation by the gas generator; a stopper coupled tothe proximal end portion of the polymer rod; and a piston-safety valvemember disposed between the gas generator and the stopper and configuredto allow gas from the gas generator to pass therethrough when the gas isat or above a predetermined pressure.
 2. The seatbelt pretensioningretractor assembly of claim 1, wherein the piston-safety valve membercomprises a piston body and a safety valve operatively coupled to thepiston body to allow the gas from the gas generator to pass through thepiston body when the gas is at or above the predetermined pressure. 3.The seatbelt pretensioning retractor assembly of claim 2, wherein thesafety valve comprises a safety valve diaphragm that is between thepiston body and the stopper.
 4. The seatbelt pretensioning retractorassembly of claim 3, wherein the piston body has a body opening formedtherethrough that is in fluid communication with the safety valvediaphragm.
 5. The seatbelt pretensioning retractor assembly of claim 4,wherein the piston body has a wall that defines the body opening andthat includes a shoulder portion at least partially surrounding the bodyopening, and wherein the safety valve diaphragm is disposed on theshoulder portion extending across the body opening.
 6. The seatbeltpretensioning retractor assembly of claim 5, wherein the safety valvediaphragm is disposed between the shoulder portion of the piston bodyand the stopper.
 7. The seatbelt pretensioning retractor assembly ofclaim 3, wherein the safety valve comprises a lip insert that interfaceswith the stopper and the safety valve diaphragm is disposed between thepiston body and the lip insert, and wherein the lip insert has a lipinsert opening formed therethrough that is in fluid communication withthe safety valve diaphragm.
 8. The seatbelt pretensioning retractorassembly of claim 7, wherein the safety valve diaphragm is disposedbetween the shoulder portion of the piston body and the lip insert. 9.The seatbelt pretensioning retractor assembly of claim 7, wherein thelip insert has a lip portion that contacts the stopper along aninterface and that defines at least one channel that allows the gas fromthe gas generator to advance downstream from the interface between thelip portion and the stopper.
 10. The seatbelt pretensioning retractorassembly of claim 1, further comprising a seal member disposed betweenthe gas generator and the piston-safety valve member.
 11. The seatbeltpretensioning retractor assembly of claim 10, wherein the seal memberand the piston-safety valve member are cooperatively configured to drivethe polymer rod through the tube in the first direction in response tothe gas from the gas generator.
 12. The seatbelt pretensioning retractorassembly of claim 11, wherein the seal member sealingly interfaces withthe piston-safety valve member.
 13. The seatbelt pretensioning retractorassembly of claim 10, wherein the seal member has a through hole influid communication with the piston-safety valve member.
 14. Theseatbelt pretensioning retractor assembly of claim 1, wherein a gap isprovided between the stopper and an inner surface of the tube thatallows the gas from the gas generator to advance past the stopper. 15.The seatbelt pretensioning retractor assembly of claim 14, wherein theouter surface of the stopper defines at least one notch that forms atleast part of the gap between the stopper and the inner surface of thetube.
 16. The seatbelt pretensioning retractor assembly of claim 14,wherein an outer surface of the stopper is substantially noncircular andthe inner surface of the tube is substantially circular so as to form atleast part of the gap between the stopper and the inner surface of thetube.
 17. The seatbelt pretensioning retractor assembly of claim 14,wherein the tube includes a projection extending within the tubeadjacent to an exit at the second end to define a constriction portionthat has an opening dimension smaller than an inside dimension ofadjacent portions of the tube, and wherein the constriction portion issized to prevent the stopper from passing therethrough.
 18. The seatbeltpretensioning retractor assembly of claim 17, wherein polymer rod has arecessed portion defining a recess that extends generally in thelongitudinal direction, and wherein the recess is aligned with theprojection in the first direction and the constriction portion is sizedto permit the recessed portion of the polymer rod to pass therethrough.19. The seatbelt pretensioning retractor assembly of claim 18, whereinthe tube includes tube vent opening proximate the exit and/or theprojection for facilitating venting the gas from the gas generator. 20.A seatbelt pretensioning retractor assembly for use in a passengervehicle, the seatbelt pretensioning retractor assembly comprising: ahousing adapted for being mounted to a vehicle structure and having aninterior cavity; a tube having an arcuate and curved shape having afirst end for fluid communication with a gas generator and a second endin fluid communication with the interior cavity of the housing; asprocket rotatably mounted to the housing and fixedly coupled to aspindle adapted for taking up seatbelt webbing during pretensioning,wherein the sprocket has a plurality of vanes; a driving elementcomprising a polymer rod having a proximal end portion that is disposedtowards the gas generator and a distal end portion that is opposite theproximal end portion, and is configured to extend in a longitudinaldirection from the proximal end portion to the distal end portion,wherein the polymer rod is disposed within the tube and is translatablethrough the tube in a first direction toward the sprocket in response toan actuation by the gas generator; a stopper coupled to the proximal endportion of the polymer rod; a piston-safety valve member disposedadjacent to the stopper on a side opposite the proximal end portion ofthe polymer rod, wherein the piston-safety valve member comprises apiston body and a safety valve operatively coupled to the piston body;and a seal member disposed between the gas generator and thepiston-safety valve member and having a through hole in fluidcommunication with the safety valve, wherein the seal member and thepiston-safety valve member cooperate to allow gas from the gas generatorto pass therethrough when the gas is at or above a predeterminedpressure.